An exhaust heat exchange apparatus 100 as a relevant heat exchanger is disclosed in PTL1. As illustrated in FIG. 1, the exhaust heat exchange apparatus 100 includes an exterior case 101, multiple tubes 110 housed in the exterior case 101, and a pair of tanks 120, 121 arranged on both ends of the tubes 110.
The exterior case 101 is provided with a cooling water inlet portion 102 and a cooling water outlet portion 103 for cooling water which is cooling fluid. Cooling water paths 104 are formed by the spaces and the like between adjacent tubes 110 in the exterior case 101. Reference sign REF in the drawings indicates the flow direction of the cooling water.
Both ends of all the tubes 110 are open in the pair of tanks 120, 121. One tank 120 is provided with an exhaust inlet portion 120a and the other tank 121 is provided with an exhaust outlet portion 121a. 
The multiple tubes 110 are stacked. As illustrated in FIG. 2, each tube 110 is formed of two flat members 110a, 110b. An exhaust path 111 is formed in the tube 110. A fin 112 is housed in the exhaust path 111 of each tube 110.
As illustrated in FIG. 3, the fin 112 is formed in a rectangular waveform. In the fin 112, multiple projection plates 113 are formed by cutting and raising at intervals in an exhaust gas flow direction S. The projection plates 113 project in a direction to block the exhaust flow in the exhaust path 111. The projection plates 113 each have a triangular shape. The projection plates 113 are arranged at a setting angle at which each projection plate 113 is inclined in a perpendicular direction to the exhaust gas flow direction S.
In the above-described configuration, exhaust gas discharged from an internal combustion engine flows through the exhaust path 111 in each tube 110. Cooling water flows through the cooling water paths 104 in the exterior case 101. The exhaust gas and the cooling water exchange heat via the tube 110 and the fin 112. When heat is exchanged, each projection plate 113 of the fin 112 disturbs the flow of the exhaust gas to promote heat exchange.
Next, promotive effect on heat exchange by the projection plates 113 will be specifically described. As illustrated in FIG. 4, when exhaust gas, which flows through the exhaust path 111, collides with the projection plate 113, the exhaust gas cannot flow straight, and thus a low-pressure region LPR is formed immediately downstream of the projection plate 113. As illustrated in FIGS. 5A, 5B, the exhaust gas collided with the projection plate 113 flows downstream as an overflow which goes around behind right and left lateral sides 113a, 113b of the projection plate 113. Since the projection plate 113 has a triangular shape, the overflow is divided into a first overflow from one lateral side 113a and a second overflow from the other lateral side 113b of the projection plate 113. Since the lateral sides 113a, 113b on both sides are inclined surfaces, the first overflow and the second overflow have a distribution such that the upper side of the inclination has a higher flow rate and the lower side of the inclination has a lower flow rate. A flow with such a distribution is drawn into the low-pressure region LPR, and thus a rotational force is applied to each of the first overflow and the second overflow which each form a spiral vortex flow as illustrated in FIG. 5C. In this manner, two spiral vortex flows are formed downstream of the projection plate 113. The two spiral vortex flows move while disturbing a boundary layer (exhaust gas stagnant layer) formed in the vicinity of the surface of the exhaust path 111, thereby increasing the heat exchange rate.